Vacuum pump construction

ABSTRACT

A vacuum pump having an improved stator support construction for preventing back flow from higher pressure to lower sections thereof, and an improved oil control system for preventing back flow of oil vapors to low pressure regions of the pump. Undesired axial leakage past the stators is prevented by providing stator support rings of a split ring construction having overlapping end portions. The rings are sized to a diameter just smaller than the smallest inside dimension of the casing and are inherently resiliently biased outwardly for snug engagement by an outer face of the ring with the entire inner periphery of the casing. The axial gaps between the overlapping end portions cause any molecules leaking between stages to be principally directed downwardly into the path of adjacent rotors for propulsion thereof downstream, rather than permitting leaking gas molecules to continue upstream along the inner surface of the casing. The open areas between overlapping sections are also spaced angularly apart from the openings in adjacent rings, to provide a labyrinthine path to prevent leakage. Further oil control is accomplished by providing an annular outlet casing in each discharge end of the pump, providing a sump for condensed oil vapors at the bottom thereof, with a line for connection with the fore pump or other vacuum source therefrom, and by disposing the outlet openings upwardly from the sump along the sidewalls of the casings.

United States Patent [72] Inventor Gordon E. Osterstrom Winnetka, Ill. [21] Appl. No. 869,806 [22] Filed Oct. 27, 1969 [45] Patented June 15, 1971 [73] Assignee Sargent-Welch Scientific Company Skokie, Ill.

[54] VACUUM PUMP CONSTRUCTION 10 Claims, 8 Drawing Figs.

[52] US. Cl 415/100, 415/199,4l5/170 [51] Int. Cl ..F04b 19/16, F04b 19/18, FOld 9/00 [50] Field ofSearch 415/97, 100, 199,90, 170, 77, 79, 90, l72;417/423; 416/199, 201

[56] References Cited UNITED STATES PATENTS 852,030 4/1907 Nussbaumer 416/198 1,793,179 2/1931 Lanterrnan et al... 415/87 2,918,208 12/1959 Becker 415/199 3,168,977 2/1965 Gamier et 417/423 3,332,610 7/1967 Osterstrom 415/172 1 FOREIGN PATENTS 1,251,606 12/1960 France 415/90 1,338,250 10/1963 France 415/100 Primary Examiner-Henry F. Raduazo Altomey-Greist, Lockwood, Greenawalt and Dewey ABSTRACT: A vacuum pump having an improved stator support construction for preventing back flow from higher pressure to lower sections thereof, and an improved oil control system for preventing back flow of oil vapors to low pressure regions of the pump. Undesired axial leakage past the stators is prevented by providing stator support rings of a split ring construction having overlapping end portions. The rings are sized to a diameter just smaller than the smallest inside dimension of the casing and are inherently resiliently biased outwardly for snug engagement by an outer face of the ring with the entire inner periphery of the casing. The axial gaps between the overlapping end portions cause any molecules leaking between stages to be principally directed downwardly into the path of adjacent rotors for propulsion thereof downstream, rather than permitting leaking gas molecules to continue upstream along the inner surface of the casing. The open areas between overlapping sections are also spaced angularly apart from the openings in adjacent rings, to provide a labyrinthine path to prevent leakage. Further oil control is accomplished by providing an annular outlet casing in each discharge end of the pump, providing a sump for condensed oil vapors at the bottom thereof, with a line for connection with the fore pump or other vacuum source therefrom, and by disposing the outlet openings upwardly from the sump along the sidewalls of the casings.

my}! l 22 lllllljl llllillll 4' j E O, 72 j 5 VACUUM PUMP CONSTRUCTION BACKGROUND AND DESCRIPTION OF THE INVENTION number of stators are arranged so that one stator is disposed adjacent and downstream of each rotor, each rotor-stator pair comprising a single stage. Since the impeller comprises a center shaft with blades radiating outwardly therefrom, and since the stators remain fixed against rotation in use, it is normal for the stator assembly to include a plurality of discs having central hubs with large diameter openings therein, and having blades extending outwardly from each continuously extending hub portion. The stators are retained in place by reason of being held adjacent the blade tips, and since rotor blade rows are interleaved with rows of stator blades of the stators must be spaced apart by a distance equal to the width of the rotor blades plus a given working clearance. Therefore, it is customary to have a support ring disposed radially outside of each rotor and of slightly greater axial width than the rotor, with the stators being held in place between adjacent rings. Thereupon, the entire array of rings and stators are axially compressed to a predetermined extent, and the stators are fixed in a desired position.

Customarily, in assembling pumps of this sort, the rotor casing is given smooth, machine finished circular bore which is intended to be perfectly cylindrical, but may be very slightly out of round from place to place around its circumference, may taper slightly, or the like. The stators are sized so that the largest diameter stator of any group of stators has an outside diameter that is slightly smaller than the minimum inside diameter of the casing, or the inside diameter of the portions of the support ring which will engage the stator. However, in providing rings for supporting'the stators, it is customary to attempt to match the outside diameter size of the ring as closely as possible with the inside diameter size of the casing. The reason for this is that if there is any peripheral spacing between the outside surfaces of the rings and the inside of the casing, a flow path will be provided through which there may be considerable gas back flow from the output end of the turbine to the input end thereof, thereby limiting the vacuum attainable with the pump. Accordingly, in the prior art, it has been common to expend significant time and effort in sizing these rings properly, lapping them for better fit, disposing them in machined grooves, or the like. In those cases in which it has not been practical to fit rings in this manner, a certain amount of leakage has been tolerated or the problem has been attacked in some other manner.

Another problem common to vacuum pumps, particularly those of the turbomolecular type, has been disposition of excess oil which collects at or near the turbine outlets. In some cases, it has been known to allow whatever oil leaks into the turbomolecular pump to travel by gravity from an outlet disposed beneath the turbine sections to the outlet connected with the fore pump associated with the turbomolecular pump. In some cases, this is not harmful, but in other cases, it is not desired to contaminate the fore pump with oil from the turbo pump, particularly when different oils are used in the different pumps. However, in any case, it is necessary to dispose of accumulated oil in some way since excesses thereof, even though -of low vapor-pressure types intended to create minimum cononly in a desired area, and which a suitable means for disposing of the oil, once collected, may be provided.

Accordingly, an object of the present invention is to provide a vacuum pump having an improved stator support ring construction.

Another object is to provide a vacuum pump in which the rings tightly engage the wall of the casing about the entire periphery thereof regardless'of dimensional variations in the rings or the casing.

A still further object is to provide a construction in which split rings may be used as stator supports without creating significant vacuum leakage between adjacent or remote stages.

Another object is to provide a vacuum pump which includes components making it possible to simplify assembly of the pump unit without sacrificing the quality thereof.

Another object is to provide an oil collector, sump, and oil removal assembly having a number of advantages.

A still further object is the provision of a pump having an oil sump associated with the gas outlet collection annulus and readily adapted for connection to a remote vacuum source for removal of oil therefrom.

The present invention accomplishes these objects and others by providing a split ring stator holder which permits the ring to be size for easy entry into the casing and to extend outwardly to engage the casing along the entire circumferential surface thereof while providing means for preventing axial flow along the portions of the pump radially inwardly of such surface, and by providing an oil collector and removal sump in the outlet annulus of the pump for connection to a remote vacuum source, and disposing the pump outlet opening in a portion of the collector annulus which is vertically spaced upwardly from the sump area.

The exact manner in which these objects, and others inherent objects and advantages of the invention are accomplished will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention and to the accompanying drawings, in which like reference numerals indicate corresponding parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view, partially in section and partially in elevation, showing a vacuum pump of the invention;

FIG. 2 is a side elevational view, on a reduced scale, of the pump of FIG. I showing portions of the oil collection system somewhat schematically;

FIG. 3 is a front elevational view of a plurality of the stator support rings embodying the present invention;

FIG. 4 is a front elevational view of one form of support ring made in accordance with the invention;

FIG. 5 is an enlarged view of a portion of the support ring of FIG. 4 taken along line 5-5 thereof;

FIG. 6 is a front elevational view of another form of support ring;

FIG. 7 is an enlarged top view of the portion of the ring of FIG. 6, taken along line 7-7 thereof; and

FIG. 8 is an enlarged view of a portion of another form of support ring of the invention, taken looking radially inwardly thereof.

Referring now to the drawings in greater detail, FIG. 1 shows an axial flow type turbine high vacuum pump 20 including a connecting flange 22 for association with an area to be evacuated, and shows that the turbine pump 20 includes a lefthand turbine portion 24 having a driven gear 26 disposed on one axial end of an impeller shaft 28, which is in turn comprised of a number of rotors 30 having a large number of blades 32 thereon. Interleaved between rotors 30 are a plurality of stators 34 having a continuously extending hub portion 36 and a plurality of blades 38, the end portions 40 of which are received between the axially directed faces 42 ofa number of annularly extending support rings 46, the construction of which will be referred to in further detail herein.

A chamber 48 lying downstream of the innermost rotor assembly 50 receives gases beingevacuated from the region associated with the flange 22. Thereupon, gases pass into an annularly extending collection chamber 52 having a flat bottom surface portion 54 and an oil collection opening 56 adjacent one end wall 58 thereof. Lying a distance vertically upwardly from the bottom surface portion 54 of the annular chamber 52 are a plurality of sidewalls 60 defining a gas outlet opening 62 in the annularly extending chamber 52. FIG. 1 shows such gas outlet opening 62 disposed only on the right-hand side of the turbine pump, but it will be understood that a similarly constructed opening is disposed in a corresponding position on the left-hand side of the pump, it being further understood that left and right-hand portions of the pump are, in respect to the internal portions thereof, mirror images of each other. That is, another turbine assembly of the same construction as the assembly 24 is located on the right-hand side of the pump 20, with gas flow through the left-hand turbine 24 being to the left as shown therein with the higher pressure chamber disposed on the axially outer end portion of the pump 20 and flow in the right-hand turbine is to the right therethrough for gas passage out the right-hand axial end of the pump 20.

FIG. 1 also shows an area 64 which is customarily occupied by a driving gear (not shown) and which includes an end plate 66 thereon for excluding liquid oil from area 64 and other areas communicating therewith. An end portion 68 of an oil vapor line 70 is attached to a passage 72 which communicates with the area 64, the opposite end portion 74 of line 70 being associated with the area 76 in which the opposite end of the impeller shaft is journaled. Referring again to the left-hand portion of FIG. 1, it may be seen that a cylindrical end portion 78 is formed on the impeller shaft 32 and rides in bearings 80 which receive a supply of vaporized oil from line 82 through passage 84.

Although a second seal 86 is provided for cooperation with an enlarged diameter portion 88 of the shaft 32, a certain amount of vapor will nevertheless escape through passages 90 and 92 and into the chamber 48, from which gas flow is directed, through one or more ports 94, into the annular chamber 52. In keeping with the invention, the bottom surface portion 54 of chamber 52 is of considerable extent, and the passages 56 provided therein will take up oil collecting by gravity and condensation for removal through sump lines 96. Referring to FIG. 2, it is diagrammatically shown that the lines 96 may terminate in remote sumps 98. Depending on the nature of the oil used in the turbine pump and in the fore pump, it may be acceptable to connect the lines 96 directly to an inlet of the fore pump for establishing a vacuum level on the lines 96 which is at least equal to the vacuum level in annular chamber 52.

On the other hand, placing the oil collection opening 56 in an area remote from the gas outlet opening' 62 insures that minimum oil vapor, and no liquid phase oil is present in the gas stream passing out through opening 62. in this connection, it may also be seen that the disposition and configuration of passages 94 is such that oil passing therethrough tends to impinge on walls 58 or the like, increasing the likelihood of condensation. In such a case, where maximum oil vapor separation from the outflowing gases takes place, it may be desirable to connect the lines 96 to a separate vacuum source, such as a very small capacity third pump unit, or from a takeoff line from the fore pump associated with the turbine pump 20, the oil accumulator outlet being thereby separated or isolated from the fore pump inlet region.

Accordingly, the provision of the gas outlet and the oil collection opening and associated lines in the relation set forth above is advantageous since it offers a choice of collecting the oil by the use of an existing fore pump or the choice ofremoving turbine pump oil by separate means.

Referring now to another aspect of the invention, FIG, 3 shows an array of support rings 46 which are adapted to be disposed within the casing 100 of the pump 20. Each ring 46 includes a principal body portion 102, and a pair of adjacently disposed end portions 104, 106. The rings 46 are made of a resilient material, and are formed so that they are self-biased resiliently outwardly so as to tend to separate the end portions 104, 106 from each other. The outer surface 108 of each ring 46 has a smooth finish thereon for an extremely close fit with the smoothly finished inwardly facing surface 110 of the easing 100. Each ring 46 is sized so that, with the rings compressed so that the end portions 104, 106 are moved into abutting relation with each other, the total outer diameter of the ring permits ring movement into the desired position of use within the casing 100, and, upon release of the compressive force, the rings expand into a position with their outer surfaces 108 engaging the inner surface 110 of the casing in a gastight relation, except at the gaps 112 separating the end portions 104, 106.

As shown in FIG. 3, the rings are disposed in an axially offset relation to one other,.occupying parallel planes, and each ring is rotated within its plane so as to move the gap 112 between adjacent end portions 104 and 106 into an angularly spaced-apart relation with respect to the axially immediately adjacent rings 46. Accordingly, as a result of this construction, each ring 46 can find its own maximum permitted diameter associated with the particular portion of the casing 100 in which it is disposed, and this will provide a snug, substantially gastight fit between its outer surface 108 and the inner surface 110 of the casing 100. Although the gap 112 is of a significant dimension, ranging from as little as a few thousandths of an inch up to as much as 0.100 inches, this does not present a serious leakage problem in use, for reasons to which reference will now be made. inasmuch as the pressure existing inside the casing 100 during operation of a vacuum pump of the type in question is always extremely low, varying from about 10" torr down to as low as 10' or even several orders of magnitude lower, molecular behavior in the pump 20 is characterized as free-molecular flow. That is, the mean free path of gas molecules in the sump is very large compared to any significant dimension of a rotor or stator blade, the support rings, or the size of any clearance in question. Accordingly, molecules flowing in this mode within the pump tend to proceed in a straight line until they strike a portion of a physical object, since the likelihood of their striking another molecule is extremely small. Accordingly, such molecules, particularly if permitted to flow alongand parallel to the inner wall 110 of the casing 100, flow as ifin a beam, traversing many if not all of the stages without striking any other gas molecules, and doing so with decreasing likelihood of collision with other gas molecules as the molecules in question pass in an upstream direction toward the lowest pressure areas of the pump. Thus, with a pump having a total pressure drop therein of 6 to 8 orders of magnitude or more, only a small net molecule flow into the low pressure regions will destroy the effectiveness of the pump, and only a relatively minute longitudinal path, if directly perpendicular to the plane of disposition of the rotors, stators and rings, will adversely affect and even nullify optimum pump performance.

On the other hand, it has been discovered that with the support ring arrangement of the invention, even though a significant gap 112 exists in some embodiments between end portions 104, 106 or rings 46 which would be permeable in the ordinary sense to a low level vacuum, the effect of the gap 112 in a turbine pump operating in the free molecular flow pressure range is somewhat surprisingly entirely different from the effect such gap would produce under different conditions. Thus, it is believed that because relatively few molecules are present, and because there is substantially no leakage permitted axially across more than one stage along the interface between surfaces 100, 110, molecules tend to flow through the gap 112 generally axially thereof at a high rate. Thereafter, having proceeded across one stage or pressure drop zone, they strike an adjacent ring 46, and if not deflected backwardly through the gap 112, have no place to go except radially inwardly where, because of its extremely high tip speed, a blade 32 will in all probability strike the molecule radially inwardly of the inner surface 114 of the stator support ring 46 and propel the molecule downstream to the next pressure stage. In

this connection, it can be seen that because of the angular offset of the gap 112 in an adjacent ring 46, the molecule cannot arrive at this gap along a straight line of propagation without traversing a chord of the cylindrical casing 100. In contrast to molecular behavior as set forth above, if a very low vacuum level were present, intermolecular collisions would be so frequent that any number of molecules, in effect, could take a path along any given surface and would be free to flow around comers, between narrow openings, and the like, simply because so many molecules would be present'that the mean free path would be totally insignificant in respect to the dimension in question, and molecular flow would be substantially exclusively affected by intermolecular collision rather than collision with portions of the pump structure.

Accordingly, in its simplest form, the invention includes rings such as those shown in FIG. 3 wherein there is no overlapping of adjacent end portions 104 and 106. Other forms of the support rings of the invention are shown in FIG. 4 and 5, for example, wherein a slit 116 formed by oppositely directed faces 118, 120, of the end portions 104, 106 extends circumferentially in the plane of the ring 46. Perpendicularly extending faces 122, 124 also partially define the end portions 104, 106 of this embodiment. A construction such as this is very effective to minimize pressure leakage to adjacent turbine stages.

FIGS. 6 and 7 show a ring construction in which the end portions 105, 106 are defined by faces 126, 128 defining an opening 130 therebetween, the faces 126, 128 extending parallel to each other and at an angle to the plane in which the ring 46 is disposed.

FIG. 8 shows one view of a pair of end portions 104, 106 in which a forked end 132 is created on end portion 104 by the provision of two extensions 136 separated by an end face 138, with the opening therefor receiving a blade portion 140 extending outwardly from the adjacent end 106. This provides an effect which is similar to that of the construction of FIG. 5, except'that the travel path thereto is somewhat more complex.

In connection with the above examples, it will be noted that a common requirement is that the ring 46 be free to expand outwardly into contact with an adjacent wall portion for tight sealing therewith. The provision of different configurations in the end portions 104, 106 permitting circumferential and axial overlapping relations therebetween further improves performance, but these elements are not always strictly necessary in accordance with the present invention.

Accordingly, it will be seen that, quite unexpectedly, outstanding leakage prevention can be obtained by providing rings which, although including significant gaps or spacing therein in certain locations, fit tightly about the remainder of the inner casing circumference and prevent axial leakage in the pump.

in view of the above, it can be seen that the present invention provides a vacuum pump having improved construction features providing a number of advantages and characteristics, including those pointed out herein which are inherent in the invention.

lclaim:

1. A vacuum pump having a cylindrical outer casing member with a radially inwardly facing inner surface portion thereon, a rotary impeller assembly disposed for rotation in said casing and having a plurality of rotor units thereon, each of said rotor units having a row of blades thereon adapted to rotate within said chamber with the tips thereof spaced from said inner wall by a given distance, a plurality of stators distance between said rotor blade tips and said casing, said rings having outer, casing engaging surfaces and adjacent end portions defining slits therein to permit radial outward expansion thereof into tight, continuous line contact between said casing-engaging surfaces and said inner surface portion of said casing, whereby substantially all of said inner surface of said casing is snugly engaged by said casing-engaging surface of said rings. 1

2. A vacuum pump as defined in claim 1 in which said adjacent end portions of said rings are disposed in axially overlapping relation to each other.

3. A vacuum pump as defined in claim 1 in which said adjacent end portions are disposed in circumferentially overlapping relation.

4. A vacuum pump as defined in claim 2 in which said adjacent end portions of said rings comprise at least partially axially directed face portions disposed at an angle in relation to the plane of said rings.

5. A vacuum pump as defined in claim 2 in which said adjacent end portions of said rings defining said'slits are spaced apart from each other along a first line extending parallel to the plane of said ring, and along second lines extending perpendicular to said plane and joining said first line.

6. A vacuum pump as defined in claim 1 in which said adjacent end portions comprise, in each ring, a fork end and a blade end in axially and circumferentially overlapping relation, said fork and blade ends providing a labyrinthine flow path for gas molecules passing therethrough.

7. A vacuum pump as defined in claim 1 in which said adjacent end portions of any one ring are angularly offset from said end portions in any adjacent ring, whereby there is no direct longitudinal path along said inner surface of said casing through several openings defined by said end portions.

8. A turbomolecular vacuum pump having a cylindrical outer casing member, a rotary impeller assembly disposed for rotation in said casing, a plurality of stator units held within said casing and being disposed in interleaved axial relation with rotor units disposed on said impeller assembly, at least one inlet and one outlet end in said casing for gas flowing therein, a generally annularly extending gas collector passage communicating with said outlet portion, said passage having an inside bottom surface portion forming an'oil collection sump, means communicating therewith for receiving oil disposed therein for removal thereof, and a gas outlet opening in said passage, said opening being defined by portions of said passage which are spaced vertically upwardly from the plane of said inside bottom surface portion.

9. A vacuum pump as defined in claim 8 in which said means communicating with said sump communicate with the inlet portion of a fore pump operatively associated with the outlet of said pump.

10. A vacuum pump as defined in claim 8 in which said means communicating with said sump communicate with the inlet portion of a vacuum source different from a fore pump associated with the outlet of said turbomolecular pump.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 584, 966 Dated June 15, 1971 Inventor(s) Gordon E. Osterstrom It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

3 Column 4, line 31, the number "10 should read lO Column 4, line 32, the number "10 should read "10 Column 5, line 27. the number "105" should read -lO4-- Signed and sealed this 26th day of September 1972.

(SEAL) Attest:

EDWARD M.FLE'I'CHER,JR. ROBERT GOT'I'SCHALK Attestlng Officer- Commissioner of Patents FORM PO-IOSU (10-69) USCOMM-DC 6O376-P69 us, GOVERNMENT PRINTING OFFICE 1969 0-366-334 

1. A vacuum pump having a cylindrical outer casing member with a radially inwardly facing inner surface portion thereon, a rotary impeller assembly disposed for rotation in said casing and having a plurality of rotor units thereon, each of said rotor units having a row of blades thereon adapted to rotate within said chamber with the tips thereof spaced from said inner wall by a given distance, a plurality of stators disposed in interleaved relation to said plurality of rotors, each of said stators having a plurality of blades thereon with the blade tips thereof substantially in contact with said inner surface, and resilient support rings disposed within said casing, said stator blade tips being engaged on axial face portions thereof by said support rings spacing said stators apart and preventing axial movement thereof, said rings having a radial thickness occupying a substantial portion of said given distance between said rotor blade tips and said casing, said rings having outer, casing engaging surfaces and adjacent end portions defining slits therein to permit radial outward expansion thereof into tight, continuous line contact between said casing-engaging surfaces and said inner surface portion of said casing, whereby substantially all of said inner surface of said casing is snugly engaged by said casing-engaging surface of said rings.
 2. A vacuum pump as defined in claim 1 in which said adjacent end portions of said rings are disposed in axially overlapping relation to each other.
 3. A vacuum pump as defined in claim 1 in which said adjacent end portions are disposed in circumferentially overlapping relation.
 4. A vacuum pump as defined in claim 2 in which said adjacent end portions of said rings comprise at least partially axially directed face portions disposed at an angle in relation to the plane of said rings.
 5. A vacuum pump as defined in claim 2 in which said adjacent end portions of said rings defining said slits are spaced Apart from each other along a first line extending parallel to the plane of said ring, and along second lines extending perpendicular to said plane and joining said first line.
 6. A vacuum pump as defined in claim 1 in which said adjacent end portions comprise, in each ring, a fork end and a blade end in axially and circumferentially overlapping relation, said fork and blade ends providing a labyrinthine flow path for gas molecules passing therethrough.
 7. A vacuum pump as defined in claim 1 in which said adjacent end portions of any one ring are angularly offset from said end portions in any adjacent ring, whereby there is no direct longitudinal path along said inner surface of said casing through several openings defined by said end portions.
 8. A turbomolecular vacuum pump having a cylindrical outer casing member, a rotary impeller assembly disposed for rotation in said casing, a plurality of stator units held within said casing and being disposed in interleaved axial relation with rotor units disposed on said impeller assembly, at least one inlet and one outlet end in said casing for gas flowing therein, a generally annularly extending gas collector passage communicating with said outlet portion, said passage having an inside bottom surface portion forming an oil collection sump, means communicating therewith for receiving oil disposed therein for removal thereof, and a gas outlet opening in said passage, said opening being defined by portions of said passage which are spaced vertically upwardly from the plane of said inside bottom surface portion.
 9. A vacuum pump as defined in claim 8 in which said means communicating with said sump communicate with the inlet portion of a fore pump operatively associated with the outlet of said pump.
 10. A vacuum pump as defined in claim 8 in which said means communicating with said sump communicate with the inlet portion of a vacuum source different from a fore pump associated with the outlet of said turbomolecular pump. 